The present invention relates to stabilizing fuel by deoxygenation, and more particularly to deoxygenation through a self-supporting porous membrane adjacent an oxygen receiving channel.
Jet fuel is often utilized in aircraft as a coolant for various aircraft systems. The presence of dissolved oxygen in hydrocarbon jet fuels may be objectionable because the oxygen supports oxidation reactions that yield undesirable by-products. Dissolution of air in jet fuel results in an approximately 70 ppm oxygen concentration. When aerated fuel is heated between 350° F. and 850° F. the oxygen initiates free radical reactions of the fuel resulting in deposits commonly referred to as “coke” or “coking.” Coke may be detrimental to the fuel lines and may inhibit combustion. The formation of such deposits may impair the normal functioning of a fuel system, either with respect to an intended heat exchange function or the efficient injection of fuel.
Various conventional fuel deoxygenation techniques are currently utilized to deoxygenate fuel. Typically, lowering the oxygen concentration to 2 ppm is sufficient to overcome the coking problem.
One conventional Fuel Stabilization Unit (FSU) utilized in aircraft removes oxygen from jet fuel by producing an oxygen pressure gradient across a membrane permeable to oxygen. Although quite effective, the gradient is produced by vacuum on one side of the membrane. As the vacuum also introduces mechanical forces on the membrane, the membrane is supported on a porous stainless steel backing plate, which is relatively expensive to manufacture and may be a diffusion barrier requiring a relative increase in the FSU size. The membrane is relatively thin (˜2–5 microns) and lacks mechanical integrity, hence the porous backing. Mechanical pumps and vacuum housings are also required to generate the pressure gradient which further increases the size and weight of the FSU.
Such thin membranes (2–5 microns) may have defects and pin-holes. Fuel may then seep through the membrane and accumulating in the backing which results in further resistance to deoxygenation.
Accordingly, it is desirable to provide a method and system for the deoxygenation of hydrocarbon fuel in an inexpensive, size and weight efficient system that avoids the relatively heavy machinery required to produce a vacuum across a relatively thin membrane.